Oil failure safety control



OIL FAILURE SAFETY CONTROL Filed July 20, 1953 l r l INVENTOR- F/g. 2 Lonzo 8. Cooper Afmm ey United States PatentO OIL FAILURE SAFETY CONTROL Lonzo S. Cooper, Piqua, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application July 20, 1953, Serial No. 368,897

1 Claim. (Cl. 184-6) This invention relates to refrigerating apparatus and more particularly to a control for preventing damage to pumps and compressors in the event of a failure of lubrication.

Lubricant failures in pumps and compressors are rare but extremely costly in large pumps and compressors.

It is an object of my invention to provide a control which will permit the starting of the pump or compressor but which will prevent continued operation in the event that the lubricant pressure does not attain or maintain the proper value within a predetermined length of time.

It is another object of my invention to provide a control for an electrically driven pump or compressor which will keep the circuit closed during the starting period but which will open the circuit within a short period of time in the event that the lubricant pressure fails to attain or maintain the proper value.

These and other objects are attained in the form disclosed by providing a normally closed bimetal switch in series with the electric driving motor. This bimetal switch is normally closed when cold, but is heated by the current flowing to the motor so that if not prevented it will open within a short period of time such as 30 seconds. A pressure operated detent responsive to the lubricant pressure of the pump or compressor is provided for preventing the opening of this bimetal switch whenever the lubricant pressure is above a predetermined pressure.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred form of the invention is clearly shown.

In the drawing:

Figure 1 is a diagrammatic view of a refrigerating system provided with a control embodying one form of my invention; and

Figure 2 is an enlarged view partly in section of the motor-compressor unit shown in Figure 1.

Referring now to the drawing there is shown a sealed reciprocating type of motor-compressor unit 20 which withdraws evaporated refrigerant from the evaporator 22 and compresses and pumps this refrigerant into a condenser 24 where it is liquefied and cooled in a receiver 26. From the receiver 26 the liquid refrigerant is conducted under the control of a suitable control valve 28 such as an automatic expansion valve into the evaporator 22. The motor-compressor unit 20 as shown in Figure 2 includes a cylinder 30 provided with a piston 32 connected by the eccentric rod 34 to an eccentric 36 upon the rotatable shaft 38. The rotatable shaft 38 is driven by an electric motor shown diagrammatically as including a main winding 40 and a phase winding 42.

The motor-compressor unit includes a lubricating system in which the eccentric shaft 38 is provided with a coaxial lubricant passage 44 having branch passages such as the branch passage 46 extending to the bearing surface of the eccentric 38 and to the passage in the eccentric rod 34 which extends to the piston pin bearings of the piston 32. The end of the eccentric shaft 38 is r. 2,768,708 1 Patented Oct. 30,- 1956 provided with another eccentric 48 operating a piston type lubricant pump 50 which through the pipe 52 draws lubricant from the lubricant sump and pumps it into the passages of the lubricating system such as the passages 44 and 46. Upon rare occasions there may be a failure of lubrication due to leakage of oil or failure of the lubricant pump 50. Under such circumstances the motor-compressor unit may be damaged in a very short time. In a comparatively large motor-compressor unit of this type, the cost of repair may be quite high and the cost of a complete replacement unit will also be very expensive. Consequently, it is desirable to provide some form of protection even for the remote possibility of a failure of lubrication.

The use of a simple oil pressure operated control to prevent the operation of the compressor upon failure of lubricant pressure is not sufficient. Since the lubricant pump 50 is driven directly from the eccentric shaft 38 there will be substantially no lubricant pressure in the lubricating system until after the compressor has been operated for a short period of time. Therefore, a simple pressure responsive device responsive to the lubricant pressure would prevent the starting of the compressor.

According to my invention in addition to the usual thermal overload switch 54 shown diagrammatically as connected in series with the supply conductor 56 and the control switch 58, I provide an additional control 60 which may be connected in series with the conductor 56 and the switches 54 and 58. This control 6:), however, may control the supply of energy through this circuit through the use of a pilot relay instead of being directly connected in the line. The control 60 includes a normally closed bimetal switch 62 which when cold keeps closed the contacts 64 and 66. It is adapted to be opened by heating through the flow of electric energy through the circuit. It may receive some of the heat through the passage of current through the bimetal and it may receive additional heat from the electric heater 68 shown diagrammatically as being connected to the anchored end of the bimetal 62. Thus when the switch 58 is open the bimetal 62 will keep the switch contacts 64 and 66 in the closed position. However, after current flows through the circuit for a short time, such as 30 seconds, the heat generated by this current in the bimetal 62 and the heater 68 will be sufficient to open the contacts 64 and 66.

Connected to the passage 44 in the eccentric shaft 38 is a pipe 70 extending to a fluid motor 72 attached to the control 60. This fluid motor 72 includes an outer casing containing a bellows having one closed end and having its open end sealed to the rim of the outer casing. The closed end of the bellows is connected directly to a rod 74 which when the pressure in the lubricant system is sufliciently high will be pressed into engagement with the bimetal 62 to hold the contacts 64 and 66 in the closed circuit position regardless of the heating effect of the current flowing through the control 60. The fluid motor 72 includes a spring 78 for retracting the rod 74 when the lubricating pressure is below a satisfactory value. This spring 78 may be adjusted by a screw 80 threaded through a part of the housing of the control 60. The pipe 70 connects to the chamber between the bellows and the housing of the fluid motor 72. When the lubricating pressure is suflicient the lubricant will impose enough pressure upon the closed end and the outside of the bellows to move the rod 74 into engagement with the bimetal 62. This will hold the contacts 64 and 66 in closed circuit position throughout the normal running of the motor compressor unit 20 as long as and whenever the lubricant pressure is at a safe value.

Whenever the motor-compressor unit 20 is stopped by the opening of the switches 54 or 58, the lubricant pressure will fall, thereby causing the fluid motor 72 to retract the rod 74. V The bimetal 62 may openthe contacts 64 and 66 for a short time after the withdrawal of the rod 74 but as soon as the bimetal 62 is cooled the contacts 64 and 66- will be reclosed. The bimetal 62 will keep the contacts 64 and 66 in the closed position as long as it is cold. Not until after the circuit has been energized a short period of time will there be sufficient heat to tend to cause the bimetal 62 to reopen. Under normal conditions, however, the heating of the bimetal 62 is slower than the built-up lubricant pressure to operate the rod 74. In this way the bimetal 62 will normally remain closed at all times other than the failure of lubricant pressure.

The phase winding 42 is connected to a running capacitor 82 and a starting capacitor 84. These two capacitors 82 and 84 are connected in parallel with each other and in series with the phase winding 42. They are connected also to one terminal of the main winding 40. The other terminals of the main and phase windings 40 and 42 are connected to the second supply conductor 86. The starting capacitors 84 are disconnected from the phase winding 42 by a normally closed voltage relay 88 having its magnetic coil connected in a shunt arrangement with the phase winding 42. This relay 88 includes a normally 25 closed contact 90 connected in series with the running capacitors 84.

Thus by my control 60 there is provided a control for 4 preventing damage to the motor-compressor unit in the event that there is a failure of lubrication.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted as may come within the scope of the claim which follows.

What is claimed is as follows:

In combination, a pump having a lubricating system, a lubricant pumping means driven by said pump for building up and maintaining a lubricant pressure in said lubricating system during the operation of the pump, electrical means including an electrical circuit for effecting the operation of the pump, a normally closed switch means in said electrical circuit having means for holding said circuit normally closed, electrothermal means for lightly applying a physical opening force to said switch means after current has flowed through said switch means for a period of time, and a fluid motor responsive to the pressure within said lubricating system and a follower operated into switch closing engagement with said switch means for preventing the opening of said switch means.

References Cited in the file of this patent UNITED STATES PATENTS Hallatz Dec. 11, 1945 

